The proposed research will investigate both the physiological role of the subfornical organ and the neural control of water intake. These studies will extend the recent discovery reported by Routtenberg and Simpson (1971) implicating the subfornical organ in the control of drinking behavior. The first experiment will investigate the effects of carbachol-induced drinking in various subcortical loci following total ablation of the subfornical organ. A silver impregnation study of the degenerating efferent projections of subfornical organ will be performed, using the Fink-Heimer (1967) method. The dipsogenic efficacy of direct application to subfornical organ of angiotensin-II, eserine, acetylcholine, and hypertonic NaCl solutions will be studied. An attempt to analyze whether subfornical organ is active in body fluid volume regulation or in osmoregulation, or both, will be performed by administering stimuli known to stimulate these receptors in both extracellular fluid compartment and cerebrospinal fluid compartment to animals in which the subfornical organ has been experimentally lesioned. By understanding the role of subfornical organ in the neural regulation of body fluid levels and drinking behavior, it may be possible to apply these new data both to clinical disorders involving such regulation and to therapeutic attempts where such regulation is manipulated.